No. 3.] GROWTH AND METAMORPHOSIS OF TORN ARIA. 439 



it arises from the oesophagus to be based on an obvious misin- 

 terpretation, and hence conclude that as yet we do not know 

 how this organ arises in Tornaria, and that all that remains is 

 to fall back upon the work of Bateson, where it is clearly 

 demonstrated that in the larva of B. Kowalevski the left enter- 

 ocoel arises as an evagination from the digestive tract. Bourne 

 is further in error, I believe, in his description of the formation 

 of the first paired body cavities (" collar cavities "). These he 

 describes as arising from two buds at opposite points on the 

 upper edge of the "intestine" in connection with the second 

 paired body cavities, and later the upper ends of these prolifer- 

 ations, pinching off, forms the first pair or collar cavities, and 

 the remaining cells form the second paired body cavities. An 

 examination of a larger number of embryos would have shown, 

 I believe, that in reality the collar cavities arise independently 

 from the posterior (last) paired cavities, by proliferation of the 

 wall of the stomach, and that the account given by Bateson for 

 B. Kozvalevski will apply in general to the Tornaria as well. 



Again in 1890 Schimkewitsch published an abstract of 

 two Russian memoirs on the homology of various organs of 

 the Enteropneusta, Echinodermata, and Chordata. He accepts 

 the Pentactula (Semon) as the type for Echinoderm develop- 

 ment. The anterior anterocosl of Tornaria and Echinoderm is 

 homologous to the anterior left body cavity of Amphioxus, 

 which also communicates with the exterior. The proboscis vesi- 

 cle of Balanoglossus is a part of the coelom, and may represent 

 the myocoel of the proboscis segment. The blood-vessels are 

 much alike in Amphioxus and Synapta (as well as in Annelids 

 and Nemertines). The gill clefts remain alone characteristic of 

 the Chordata. The gonads of Annelids, Nemertines, Entero- 

 pneustra, Amphioxus, and Echinoderms are formed on the same 

 type, and the genital openings of Balanoglossus and Nemertines 

 are probably homologous with the ectodermal part of the seg- 

 mental organ. The nerve tube of Balanoglossus corresponds to 

 that of the Chordata. 



In their LelirbucJi d. Entwicklungsgeschichte, etc., Korschelt 

 and Heider state in their general summary of the groups that a 

 comparison of the Tornaria with the Echinoderm larva is diffi- 

 cult to carry out, inasmuch as there is no homologue for the 

 circular band of Tornaria. The latter has an apical plate and 



